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  1. #1
    Join Date
    Sep 2007
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    Default Dual Insulation?

    My 10-yr-old house has poor AC in the top floor (basement, main, top floor). I checked the attic and found it to be 130+. The AC ducts for the top floor go through the attic. They are insulated, but I wonder if cooling the attic will help.

    The attic ventilation is also very poor. For ~2400 sq ft, there is one gabel vent on the south about 1 foot sq. There are three skylight vents, but for openings, the builders simply pounded a fist-sized hole in the roof where each vent was attached.

    I've cut the skylight vent openings to match the size of the vents. There is about 2 feet deep of insulation sprayed on the floor. I'm wondering if 1) do I need another gabel vent on the north side of the attic, 2) should I install an attic fan, and 3) would adding rolls of batted insulation along the roof help?

    In other words, I'd have dual insulation in the attic: the stuff sprayed on the floor and rolls up over head... (I live out West.)

  2. #2
    Join Date
    Aug 2007
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    21

    Default Re: Dual Insulation?

    Gable vents are frowned upon here. (mi) As you want soffit vents for intake and ridge vent or cans for exhaust. You don't mention if you have any soffit vents or even an overhang.

  3. #3
    Join Date
    Aug 2007
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    Default Re: Dual Insulation?

    DNufer... there does seem to be a couple of issues here.

    The first issue addressing the poor A/C has some questions that come to mind. Is the air hander for the A/C located in the basement? If that's the case that's quite a run for ducting and I would have to question if there is enough CFM ( cubic feet per minute ) supplied to the top floor. This would have to be checked to see if the blower is putting out enough and the ducting is sized properly. Also is there sufficient cold air return for the top floor? If not correct any of these variables would contribute to poor cooling on the top floor . Remember cold air doesn't rise very well so if it has to move one , two or three levels to come out of the ceiling on the top floor that's a considerable amount of effort.

    It might be in your best interest to have a professional come out and check for enough supply air and return CFM.

    You say the insulation in your attic is 2 feet thick ... that's very good if you consider a rough guide of R5 / inch x 24 inches = R120.

    As for the venting of the attic space there should be some soffit venting included to create an air circulation circuit. It wouldn't hurt to have another gable vent at the other end and combined with the soffit vents this will help offset the need for more roof vents .

    As for attic fans there is some popularity for them but there has been research done by our National Research Council up here that has found they can actually create negative pressure in the home. This is from the attic exhaust fan pulling up air from the home through any voids in the structure or things like poorly sealed ceiling fixtures , vent stacks , etc..

    In places like Australia it's fairly common for them to include a layer of insulation directly under the roof sheathing to help with preventing heat penetrating the attic space. Of course they wouldn't have the worry of having the air gap under the roof sheathing since they don't have the winter cold.

  4. #4
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    Default Re: Dual Insulation?

    I guess I shouldn't generalize that statement for the whole continent rather I had based it on the account of a good friend living and working in various parts of Australia.

    I guess we'll see more showings from Australia in winter Olympic events.

  5. #5
    Join Date
    Sep 2007
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    4

    Default Re: Dual Insulation?

    FYI, I also posted a reply to a posting I made about a problem with my ducts. From what I've heard in this thread as well as that one, I'm going to have an HVAC guy come and check it all out so I can get things fixed.

    Meanwhile, I'll add that the AC blower is on the main floor outside the house. (At least, I assume that big, nasty, noisy box is the blower. If it's not, then it would have to be in the basement.) I've long suspected that there are too many floors for one blower.

    We'll probably fix the most serious problems now (the ventilation issues) and budget a boost to the AC system in for next year.

  6. #6
    Join Date
    Aug 2007
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    Default Re: Dual Insulation?

    Quote Originally Posted by DNufer View Post
    FYI, I also posted a reply to a posting I made about a problem with my ducts. From what I've heard in this thread as well as that one, I'm going to have an HVAC guy come and check it all out so I can get things fixed.

    Meanwhile, I'll add that the AC blower is on the main floor outside the house. (At least, I assume that big, nasty, noisy box is the blower. If it's not, then it would have to be in the basement.) I've long suspected that there are too many floors for one blower.

    We'll probably fix the most serious problems now (the ventilation issues) and budget a boost to the AC system in for next year.
    The device outside you are referring to is the A/C condenser though it has a fan this is not the blower for the inside of the house. The air handler is actually in your basement ( the furnace ) as per your other post I came across regarding the fresh air intake from the attic. You definitely have some unusual issues that needs to have someone come out and check for you.

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